<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      list-style: none;
    }

    .main {
      height: 100%;
      width: 100%;
    }

    .r_nav {
      position: absolute;
      right: 0;
      top: 50%;
      transform: translateY(-242px);
      /* margin-top: -242px; */
      width: 200px;
      height: 484px;
      background-color: skyblue;
    }
  </style>
</head>

<body>
  <div class="main">
    <div class="r_nav"></div>
  </div>
</body>

</html>